Impact of the Physiological Effects of Aging on the Pharmacokinetics and Pharmacodynamics of Systemic Lung Cancer Treatment

Pharmacokinetics includes the study of the mechanisms of absorption and distribution of an administered drug, the rate at which a drug action begins and the duration of the effect, the chemical changes of the substance in the body, and the effects and routes of excretion of the metabolites of the drug. Pharmacodynamics is the study of the biochemical and physiological effects of drugs on the body and the relationship between drug concentration and effect. Overall, pharmacokinetics is the study of what the body does to a drug, whereas pharmacodynamics is often summarized as the study of what a drug does to the body. Pharmacokinetic interactions involve one drug or substance altering the absorption, distribution, metabolism, or elimination of another drug or substance. A common example of a pharmacokinetic interaction occurs when two drugs compete for the same metabolic pathway. When the pathway becomes saturated neither drug can be metabolized fully, which results in higher serum concentrations of the agents and can lead to clinically unfavorable consequences. Pharmacodynamic interactions occur when two drugs or substances have similar molecular targets, but do not affect the pharmacokinetic parameters of each other. Pharmacodynamics is related to the pharmacological activity of the interacting drugs, e.g., synergism, antagonism, altered cellular transport, and effect on the receptor site. When two or more drugs that have similar pharmacodynamic activity are coadministered, the additive effects might result in an excessive response or toxicity. Pharmacodynamic interactions occur when two or more drugs have mechanisms of action that result in the same physiological outcome.